1. Field of the Invention
The present invention relates to a force sensor chip and a force sensor, and particularly relates to the force sensor chip and the force sensor which detect an applied external force using a plurality of strain resistance elements.
2. Description of Related Art
Conventionally, a multiaxial force sensor which precisely detects a strength and direction of an applied external force is used, for example, for industrial robots for correctly and flexibly controlling the external force applied during operations.
For example, a multiaxial force sensor which utilizes a property of a strain resistance element (piezoresistive element) is known, in which the resistance changes by a micro-strain (compressive, tensile) due to an applied external force. The sensor is disclosed, for example, in Japanese Laid-open Patent Publication Numbers 2003-207405 and 2003-254843.
The multiaxial force sensor includes a force sensor chip fabricated on a semiconductor substrate through a semiconductor fabrication process and an attenuator formed by a metal member for fixing and housing the force sensor chip.
Practically, the force sensor detects a strength and direction of an external force by appropriately arranging a plurality of strain resistance elements around an action portion to which the applied external force is transmitted and by detecting changes of resistances of the strain resistance elements as electric signals. Meanwhile, if the applied external force is directly transmitted to the strain resistance elements, the force sensor chip may be damaged when the force is too large. Therefore, an attenuator is disposed for suitably responding to various kinds of external forces and transmitting the external forces to the force sensor chip by appropriately attenuating the external forces.
In a conventional force sensor chip, a plurality of strain resistance elements are often arranged on a semiconductor substrate in two directions orthogonally crossing each other. On the other hand, the semiconductor substrate is manufactured to have a surface with some crystal orientation. However, a small difference in crystal orientation is produced between the surface and the crystal orientation by a semiconductor substrate manufacturing process. If a plurality of the strain resistance elements are arranged orthogonally on the semiconductor substrate described above, a physical constant such as a piezoresistive coefficient becomes different among the elements, thereby resulting in non-uniform characteristics among the strain resistance elements. If the force sensor chips described above are applied to the multiaxial force sensor, a correction of non-uniformity is required among detected values because of the non-uniform characteristics among the strain resistance elements, thereby resulting in complexity of signal processing.
It is, therefore, desirable to provide a force sensor chip and a force sensor which can improve uniformity of characteristics among a plurality of strain resistance elements.